The effect of exposure concentration, duration, and ventilation rate on ozone absorption during continuous inhalation exposure

Ozone (O₃), a component of urban smog, causes lung irritation upon inhalation and is a significant public health concern. Studies of the effect of O₃ inhalation on humans typically relate exposure directly to response, with little or no consideration of the actual uptake of O₃. We hypothesize that duration of exposure, inhaled concentration, and respiratory flow rate are all factors that might affect the uptake of O₃ in the respiratory tract, causing a nonlinear relationship between exposure and dose. To test this hypothesis, we have designed a high-speed ozone analyzer which is capable of sampling and monitoring breath-by-breath ozone concentration in real-time in exercising individuals. We measured the fraction of inhaled O₃ which was retained, Λ, in eight human subjects during continuous exposure in each of four sessions with O₃ concentrations of either 0.2 or 0.4 ppm, exposure duration of 30 or 60 min., and target ventilation rates of 20 or 40 Lpm. Our results indicate that O₃ uptake is proportional to ventilation rate, exposure time, and inhaled concentration such that Λ had a value of 0.86±0.06 (mean±SD) for all the subjects we tested